1. Field of the Invention
The present invention relates to a cutting insert for a radius cutter and a indexable-insert radius cutter removably fitted with said tip.
2. Description of the Related Art
Contour line cutting work is performed mainly by means of a ball nose end mill, for example. However, the ball end mill has a semicircular cutting edge, and the cutting speed at the distal end portion of the cutting edge, that is, in the vicinity of the tool axis, is very low. Thus, the ball nose end mill considerably varies in cutting resistance between the vicinities of the outer periphery of the cutting edge and the distal end of the cutting edge, so that its cutting conditions are unstable.
In forming a flat surface by means of the ball nose end mill, moreover, the rate of pick feed (with a pitch perpendicular to the tool axis) cannot be increased. Since the cutting speed near the distal end of the cutting edge is low, moreover, there is a problem that a workpiece adheres to the cutting edge.
In a radius end mill, on the other hand, a cutting edge in the form of a substantially quarter circular arc is located on the outer periphery of the distal end of a cylindrical tool body. Thus, the radius end mill has no cutting edge near the axis of the tool body, so that the minimum cutting speed of the cutting edge is high. Accordingly, the radius end mill is characterized in that it is not susceptible to the aforementioned problems of the ball nose end mill.
In forming a flat surface by means of the radius end mill, moreover, the rate of pick feed can also be increased to ensure high-efficiency machining. Thus, radius end mills have recently been used with increasing frequency.
Further, there are indexable-insert radius end mills wherein a cutting edge is removably mounted on a tool body. For example, a indexable-insert radius end mill described in Jpn. Pat. Appln. KOKAI Publication No. 2005-40924 is frequently used for rough cutting work of mold and can ensure an effective reduction in tool costs.
If a feed rate, such as the rate of pick feed, is increased, the cutting resistance also increases. Thereupon, cutting edges are liable to chipping or fracture, so that the life of cutting edges may be shortened. If the pick feed rate is increased, moreover, chips for each cutting edge increase. In consequence, chips cannot be discharged smoothly, so that a tool may bite the chips.